A first batch of explosives planted inside a parked pickup truck ripped through an area of restaurants and shops in a busy area of Yala city, a main commercial hub of Thailand’s restive southern provinces, said district police chief Col. Kritsada Kaewchandee.

About 20 minutes later, just as onlookers gathered at the blast site, a second car bomb exploded, causing the majority of casualties. Eleven people were killed and 110 wounded by the blasts.

More than 5,000 people have been killed in Thailand’s three southernmost provinces — Narathiwat, Pattani and Yala — since an Islamist insurgency flared in January 2004.

“This is the worst attack in the past few years,” said Col. Pramote Promin, deputy spokesman of a regional security agency. “The suspected insurgents were targeting people’s lives. They (chose) a bustling commercial area, so they wanted to harm people.”

Most attacks are small-scale bombings or drive-by shootings that target soldiers, police and symbols of authority, but suspected insurgents have also staged large attacks in commercial areas.

A blast also occurred Saturday at a high-rise hotel in the city of Hat Yai, in the nearby province of Songkhla. Officials had initially attributed that blast to a gas leak, saying it was unrelated to the attacks blamed on insurgents. But after inspecting the hotel’s underground parking lot, authorities found a severely damaged sedan and a hole created by the explosion’s impact.

The midday explosion at the 405-room Lee Gardens Plaza Hotel, where throngs of Malaysian and Singaporean tourists spend their weekends, killed three people and caused about 230 injuries, mostly from smoke inhalation, said police Lt. Puwadon Wiriyawarangkun.

Regional police chief Lt. Gen. Jakthip Chaijinda said the Hat Yai incident “is likely related to what happened in Yala and might have been plotted by the same group of insurgents.”

Police said the blast that occurred at the underground level of the hotel ripped the building’s cooking gas pipeline, causing a fire that sent smoke spiraling into the upper floors and trapping many people in their rooms until rescuers came. One of the fatalities was identified as a Malaysian tourist.

A McDonald’s restaurant on the hotel’s ground floor appeared to have suffered heavy damage from the blast.

The hotel was also targeted in 2006, when four people, including a Canadian man, were killed by six bombs that had been planted on Hat Yai’s main street. Hat Yai and the rest of Songkhla province have generally been spared the violence that has wracked Narathiwat, Pattani and Yala.

The Yala bombings occurred on a road that was previously heavily guarded by checkpoints and closed to traffic to ensure safety. But the security was lifted in 2011 after local vendors said the measures harmed their businesses.

Initial accounts of the Yala attack cited three blasts with explosives planted in cars and motorcycles, but officials later corrected themselves.

In October last year, suspected militants staged coordinated attacks at more than 30 spots across Yala city, killing three people and injuring more than 50. A month earlier, a trio of bombs hidden in vehicles hit a busy section of Sungai Kolok in Narathiwat province, killing four people and leaving more than 60 wounded.

Thai authorities have imposed a state of emergency since 2005 that gives security forces special powers to arrest and detain suspects in the three provinces. But the decree and a massive security presence have failed to curb the violence and little is known about the militants or their goals.

The insurgents have made no public pronouncements but are thought to be fighting for an independent Muslim state. The area used to be an Islamic sultanate until it was annexed by Thailand in the early 20th century.

Yala, Narathiwat and Pattani are the only Muslim-dominated provinces in the predominantly Buddhist country. Muslims in the area have long complained of discrimination by the central government.